A federal judge has granted a new date to sentence Mohamed Mohamud, a postponement shrouded in secrecy.

A Portland jury convicted Mohamud in January for attempting to detonate a bomb at the city's 2010 holiday tree-lighting ceremony, and the date for his sentencing was set for Sept. 6.

Late last month, prosecutors filed motions to postpone the sentencing and -- in an unusual twist -- file the rationale for that postponement under seal. Mohamud's defense team did not oppose the motions, and the reasons for the schedule change were not made public.

U.S. District Judge Garr M. King set Mohamud's sentencing for the morning of Dec. 18.